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Multicolored maps on topographic bases in 4- by 6-degree quadrangle units; scale 1:1 million; show regional distribution of Quaternary (surficial) geologic materials in the conterminous United States and adjoining areas.

The Quaternary Geologic Atlas is a coordinated series of surficial geologic maps that will, when completed, cover the entire conterminous United states at a scale of 1:1 million. The Atlas is a product of collaboration among State geological surveys, universities, and the United States Geological Survey (USGS).

Maps in the Quaternary Atlas show the regional distribution of geologically young surficial deposits such as glacial, alluvial, eolian, lacustrine, marine, and landslide deposits. In addition, the maps show the distribution of slope and upland deposits that have not been mapped widely in the past, such as colluvium, residuum, and saprolite. These materials, which are the products of weathering and have many different physical characteristics, are classified, mapped, and described on the basis of unpublished interpretations, published and unpublished subsoil data, and the distribution of bedrock parent materials.

Map units are differentiated on the basis of a combination of criteria such as lithology, texture, genesis, stratigraphic relations, and age. Some geomorphic features, such as moraines, are distinguished as map units. Erosional landforms, such as stream terraces, are not distinguished and differentiation of sequences of alluvial deposits of different ages is not possible at a scale of 1:1 million. Most landslides are too small to be shown at this scale, but areas in which landslides are present are distinguished as map units. Each map is accompanied by a detailed description of map units.

For practical purposes, the maps are surficial materials maps. They are not maps of soils as soils are recognized and classified in pedology or agronomy. Rather they are generalized maps of soils as recognized in engineering geology, or of subsoils or parent materials from which pedologic and agronomic soils are formed.

The topographic base maps for the Quaternary Geologic Atlas are 4- by 6- degree quadrangles from the International Map of the World Series. Maps of the Atlas are in the I Series and each is numbered I-1420, with a suffix corresponding to the International Map of the World identification code for the quadrangle represented; for example, I-1420 (NJ-17) for the Chesapeake Bay quadrangle.